Math 64 Chapter 8

Admixture Calculations

Intravenous Medications

IV – Intravenous, a drug that is in a liquid, or liquid-like, state that is administered with a syringe and needle.

  • Just under the skin, subcutaneous (SQ)
  • Into the muscle, intramuscular (IM)
  • Into the vein, intravenous push (IVP)
  • Into the vein, slowly infused through dilution in an IV fluid

Dosage units:

  • Milligrams
  • Grams
  • Milliequivalents (mEq)
  • Units

milliequivalents

Milliequivalents indicate a type of measurement. Your text says,

“The milliequivalent is a measure of the ratio between a molecule’s weight and it valence electrons.”

This definition can also apply to an equivalent. From what I have read, the units for equivalents are generally g. The units for milliequivalents are generally mg.

Just looking at the word “milliequivalent” should tell you that it is equal to 1000th of an “equivalent.” Here’s the bottom line:

Let’s say the equivalent for a compound is 14.83g.

The milliequivalent (1000th of that) would be 0.01483g, which we would probably convert to mg and get 14.83mg.

  • Molecule: a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
  • Weight of a Molecule (aka “formula weight” or “atomic weight”): the mass of one mole of a substance. For potassium chloride, the formula weight is 74.5513 g.
  • The valence of a molecule is the number of electrons on the outer ring. Potassium chloride has a valence of 1.

Like with most medications, milliequivalents come in different strengths.

I like to think of milliequivalents as “replacement chemicals” needed when a person is lacking in a certain “something” in their system. Electrolytes seem to be the most common.

I have also heard “milliequivalents” used with respect to medications. For example, let’s say you are taking two separate prescriptions for the same ailment (similar active ingredients, but one being stronger than the other). Separately, the maximum dose is easily known; but taken together, a doctor would have to determine their “equivalency” to each other to avoid an overdose.

Practice Problems

#1 A physician ordered 15 mEq of potassium chloride in normal saline (NS) 100 mL. How much potassium chloride will be added to the NS? Potassium chloride is available as 2 mEq/mL.

#2 Potassium phosphate 60 mEq/1000 mL is ordered. The patient has 750 mL remaining in the current IV bag. How much should be added to this current IV bag? Potassium phosphate is available as 4.4 mEq/mL.

Because the admixture is going in 750 mL instead of 1000 mL, you need to reduce the amount of admixture. After you figure the new level of admixture, calculate the number of mL needed of the stock admixture to get the strength needed.

Units

In mathematics “units” are used when we don’t know the real units. If I was finding the area of something and didn’t know the measurements units, I would answer with something like 54 sq units.

In pharmaceutical, it is completely different.

  • From your text: “The unit is a measure of a particular medication’s activity based on a test system for that specific agent.”
  • From a specifically defined amount of anything subject to measurement, as of activity, dimension, velocity, volume, or the like.
  • Example: a unit of insulin is not measured in the same way as a unit of heparin or vitamin E.

Insulin is 100 units/mL

Practice Problems

#3An order for regular insulin calls for 12 units/100 mL. The patient has a 500 mL bag of NS currently hanging. How many units of insulin must be added? How many milliliters of insulin are needed for the dose? Insulin is available as 100 units/mL.

The idea here is to make maximum use of the NS (for each 100 mL in the bag, 12 units of insulin is desired).

TPN Solutions

Total parental solution (TPN) is an IV that provides nutrition to patients who cannot eat normally. They have multiple additives customized to the patient.

Solution base Possible Additives

Dextrose solution (sugar)Potassium
Amino Acid solution (protein)Sodium
Calcium
Multiple Vitamins

1) Volume not known.

Potassium chloride (KCl) 40 mEqstock = 2 mEq/mL

How much of the stock solutions is needed?

2) Volume known. Final volume of the TPN solution is 2500 mL.
KCl 30 mEq/1000 mLstock = 2 mEq/mL
How much of the stock solution is needed?
First determine the amount of mEq needed then the mL of stock.

IV Flow Rates

Can be run over a specific time (20 min) or at a continual rate (100 mL/hr).

An IV is running at 125 mL/hr. What is the mL/min.

Drop Sets

IV tubing is called drip sets, drop sets, microdrip sets. Each delivers A SET NUMBER OF DROPS IN 1 ml.

The most common rates are 10, 15, 20, 60 drops per milliliter (gtts/mL). gtts comes from a Latin word (guttae meaning drop). Please remember, gtts/mL are units.

  • They represent a rate of how many drops per mL.
  • gtts can be used with time (minutes). gtts/min is the number of drops per minute (also a rate).

The formula for finding drip rate (with respect to time) is:

Example 10AAn IV is being administered at 75 mL/hr. What is the gtts/min for a 20 gtt/mL tubing?

There is no need to include units in the equation.

Example 12AAn IV is running at 30 gtts/min through a 10 gtts/mL tubing. How many milliliters will be needed for 24 hrs?



Example 12BDopamine 400 mg in 240 mL is running at 5 gtts/min through a 20 gtts/mL tubing. How much drug is administered per minute?

Practice Problem 8.2 #10

Dopamine 800 mg in 250 mL is ordered. The dose is 5 mcg/kg/min. The patient weighs 75 kg. The nurses use a 15 gtts/mL tubing.

  1. What is the mg/min?
  1. What is the mg/hr?
  1. What is the mL/hr?
  1. What is the gtts/min?

Homework: All the odd in the Chapter 8 Quiz. Consider doing the evens (you do not have to turn in the evens).

Milliequivalents

1 equivalent = 1000 milliequivalents

Mostly used with electrolyte solutions (may be used for treating or preventing dehydration).

Nate Morrow Contributor Medically Reviewed

Ever stopped and wondered while chugging your favorite sports drink, “What the heck are electrolytes, anyway?” We all know they’re important for hydration, especially in athletics, but why? Aren’t they just salts?

In terms of how our bodies function, electrolytes are anything but “just”…

Your body is a complex and carefully-balanced superhighway of cells, tissues, and fluids that, almost every second, directs an incomprehensible array of electrical impulses. This is only possible because those cells, tissues, and fluids thrive in a homeostatic environment where they conduct electricity well enough to carry the signals to their intended destinations.1

The key to maintaining this conductive superhighway lies with our friend: the electrolyte.2

What Are Electrolytes?

When dissolved in fluid, salts tend to break apart into their component ions, creating an electrically-conductive solution. For example, table salt (NaCl) dissolved in water dissociates into its component positive ion of sodium (Na+) and negative ion of chloride (Cl-). Any fluid that conducts electricity, such as this new saltwater solution, is known as an electrolyte solution: the salt ions of which it’s composed are then commonly referred to as electrolytes.

There are several common electrolytes found in the body, each serving a specific and important role, but most are in some part responsible for maintaining the balance of fluids between the intracellular (inside the cell) and extracellular (outside the cell) environments. This balance is critically important for things like hydration, nerve impulses, muscle function, and pH level.

An electrolyte imbalance, whether too much or too little, can be quite detrimental to your health. Muscle contraction, for example, requires calcium, potassium and sodium; deficiency may result in muscle weakness or severe cramping. Too much sodium, on the other hand, can cause high blood pressure and significantly increase your risk of heart disease. Don’t get too worried about maintaining your electrolytes; luckily, electrolyte levels are mostly determined by food and water consumption so keeping the right balance simply comes down to proper nutrition.

Now let’s take a look at the seven major electrolytes found in the human body to get a better idea of what each does and why it’s important.

7 Major Electrolytes & Their Function
Here’s a closer look at the 7 major electrolytes:
Sodium (Na+)Chloride (Cl-)Potassium (K+)Magnesium (Mg++)
Calcium (Ca++)Phosphate (HPO4–)Bicarbonate (HCO3-)

milliequivalent

(mEq) [mil″e-e-kwiv´ah-lent]

one thousandth (10−3) of a chemical equivalent (see equivalent weight). Concentrations of electrolytes are often expressed as milliequivalents per liter, which is an expression of the chemical combining power of the electrolyte in a fluid.